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Re: Validating files and directories

From: Greg Wooledge
Subject: Re: Validating files and directories
Date: Sat, 13 Nov 2021 08:27:37 -0500

On Sat, Nov 13, 2021 at 12:50:25PM +0000, Chris Elvidge wrote:
> On 13/11/2021 06:19 am, Alex fxmbsw7 Ratchev wrote:
> > -a is like && 'and'
> > -e means existing at all
> > if -e is true it may be -d -f or fifo or socket, or such
> I suggest you reread 'help test'

He probably won't.  And that protonmail user probably won't.  So let's
be explicit here:

unicorn:~$ help test | grep -e -a -e -e
      -a FILE        True if file exists.
      -e FILE        True if file exists.

The unary -a and -e operators in test are identical in bash.

If you want more backstory, check the POSIX test(1p) man page:

       but there was no easy way to determine that an existing file was a reg‐
       ular file. An early proposal used the KornShell -a  primary  (with  the
       same  meaning),  but this was changed to -e because there were concerns
       about the high probability of humans confusing the -a primary with  the
       -a binary operator.

The POSIX test command only supports the unary -e operator, and does not
list a unary -a operator.  (And the binary -a is considered obsolescent.)

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